SAE 4340 Round Bars

SAE 4340 hot rolled round bar is a nickel chromium molybdenum through-hardening alloy steel bar used for shafts, gears and axles.

16 to 125 mm Alloy steel Made to order

HOT ROLLED ROUND BARS

SAE 4340 hot rolled round bar

SAE 4340 hot rolled round bar is a nickel chromium molybdenum alloy steel rolled to round section and bought for parts that must harden right through. The steel carries about 0.4 percent carbon with nickel, chromium and molybdenum added, and that combination lets a section reach full hardness at its centre after quenching and tempering, not only at its skin. SAE 4340 is the SAE designation of the EN 24 recipe, and the same steel appears in European standards as 34CrNiMo6, material number 1.6582. Against SAE 4140, which has chromium and molybdenum but no nickel, 4340 holds its strength through thicker bars; on light sections, or where the strength asked for is lower, 4140 is the plainer choice. Grades with more nickel sit above it. The steel has no corrosion resistance and rusts like plain carbon steel.

The bar is supplied annealed, normalised, or hardened and tempered to a BS 970 condition such as T, U or V, so a part can be machined soft and treated later, or bought already at strength. Annealed bar cuts predictably; in the harder conditions cutting is slower and tooling wears faster. Hardening is by quenching in oil and tempering, and the tempering temperature sets the final strength. Welding needs preheat and a temper afterwards, because the carbon and alloy content leaves the weld zone prone to cracking. Parts turned from this bar include crankshafts and axle shafts, gear and pinion blanks, machine tool spindles and drive shafts, and lengths that a customer forges into tooling and dies.

Composition limits in weight percent are carbon 0.38 to 0.43, manganese 0.6 to 0.8, sulphur 0.04 maximum, phosphorus 0.035 maximum, silicon 0.15 to 0.35, chromium 0.7 to 0.9, nickel 1.65 to 2.0 and molybdenum 0.2 to 0.3.

SPECIFICATION

SAE 4340 hot rolled round bar supply conditions

Size range: 16 mm - 125 mm (5/8" - 5")
Length: Up to 8 metres
Tolerances: EN10060
Heat treatment: Soft annealing or normalising; oil or water quenching and tempering
Grade: SAE 4340 (4340, 34CrNiMo6, EN 24, 1.6582)
Family: Alloy steel
Supply: Made to order in this grade; every published size of the form

Composition of SAE 4340

Element	Symbol	Minimum %	Maximum %
Carbon	C	0.38	0.43
Manganese	Mn	0.6	0.8
Sulphur	S		0.04
Phosphorus	P		0.035
Silicon	Si	0.15	0.35
Chromium	Cr	0.7	0.9
Nickel	Ni	1.65	2.0
Molybdenum	Mo	0.2	0.3

Composition, weight percent, balance iron. From the Laxcon Steels grade reference.

Equivalents of SAE 4340

Standard	Designation
DIN	34CrNiMo6
British EN	EN 24

Equivalence means nearest counterpart, not identity: each standards body sets its own composition window, so the limits of the standard named on the order govern.

Governing standards

EN 10083-1: Steels for quenching and tempering, part 1: general technical delivery conditions for the bars, rods and sections supplied for heat treatment.
EN 10083-3: Steels for quenching and tempering, part 3: technical delivery conditions for alloy steels, 42CrMo4 and 34CrNiMo6 among them.
BS 970-1: Wrought steels for mechanical and allied engineering purposes, part 1: the British numbering behind the EN and M designations and the R to Z heat treatment conditions.
ASTM A29/A29M: Steel bars, carbon and alloy, hot-wrought: general requirements for delivery, the base every carbon and alloy bar order inherits.
ASTM A322: Steel bars, alloy, standard grades: the composition tables for the SAE alloy grades supplied as bar.
EN 10060: Hot rolled round steel bars for general purposes: dimensions and tolerances on shape and dimensions.
NACE MR0175 / ISO 15156: Materials for use in H2S-containing environments in oil and gas production: the sour-service limits on hardness and condition.
EN 10204: Metallic products, types of inspection documents: the 2.2 test report and the 3.1 and 3.2 inspection certificates a purchase order can call for.

Weight per metre

Diameter (mm)	kg per metre	Metres per tonne
16	1.58	633.5
17	1.78	561.2
18	2.00	500.6
19	2.23	449.3
20	2.47	405.5
21	2.72	367.8
22	2.98	335.1
23.2	3.32	301.3
24	3.55	281.6
25	3.85	259.5
26	4.17	239.9
27	4.49	222.5
28	4.83	206.9
30	5.55	180.2
32	6.31	158.4
34	7.13	140.3
36	7.99	125.1
37	8.44	118.5
38	8.90	112.3
40	9.87	101.4
42	10.88	91.9
45	12.49	80.1
47	13.62	73.4
48	14.21	70.4
50	15.41	64.9
53	17.32	57.7
56	19.34	51.7
57.5	20.39	49.1
60	22.20	45.1
63	24.47	40.9
66	26.86	37.2
67.5	28.09	35.6
70	30.21	33.1
73.5	33.31	30.0
75	34.68	28.8
77.5	37.03	27.0
80	39.46	25.3
83	42.48	23.5
85	44.55	22.4
88	47.75	20.9
90	49.94	20.0
93	53.33	18.8
95	55.65	18.0
98	59.22	16.9
100	61.66	16.2
105	67.98	14.7
106	69.28	14.4
110	74.61	13.4
115	81.54	12.3
120	88.79	11.3
125	96.34	10.4

Density 7.85 g/cm³, diameter squared x 0.006166. Sizes are the published range at the nominal diameters shown.

Ordering SAE 4340 hot rolled round bar

An enquiry for this bar states the grade with its governing standard (SAE 4340 to SAE J404, 34CrNiMo6 to EN 10083-3, or EN 24 to BS 970), the condition required, the diameter and the tolerance it is held to under EN 10060 or ASTM A29, the cut length, the quantity, the EN 10204 certificate type, and any test called for, such as ultrasonic examination or a handheld alloy check by PMI. Laxcon Steels rolls the bar to order.